1. Field of the Invention
The present invention relates to a blood pressure monitor apparatus which monitors a blood pressure of a living subject, based on information on a pulse wave which propagates through an artery of the subject.
2. Related Art Statement
There is known, as information on a pulse wave which propagates through an artery of a living subject, a pulse-wave propagation time DT or a pulse-wave propagation velocity V.sub.M (m/s). The pulse-wave propagation time DT represents a time in which a pulse wave propagates between predetermined two different locations of the subject. Additionally, there is known that the pulse-wave propagation information is, within a predetermined range, substantially proportional to a blood pressure BP (mmHg) of the subject. Therefore, there has been proposed a blood pressure monitor apparatus which determines, in advance, coefficients .alpha., .beta. in an expression: EBP=.alpha.(DT)+.beta. (where a is a negative value) or EBP=.alpha.(V.sub.M)+.beta. (where a is a positive value), based on a measured blood pressure value BP of the subject and an obtained pulse-wave propagation time (DT) or an obtained pulse-wave propagation velocity (V.sub.M), determines an estimated blood pressure value EBP of the subject, based on each set of subsequently obtained pulse-wave propagation information, according to the above mentioned expression, and starts a blood pressure measurement using a cuff upon detection of abnormality of the estimated blood pressure value EBP.
In the case where a relationship between blood pressure and pulse-wave propagation information as indicated above is determined, at least two combinations of blood pressure value and pulse-wave propagation information are needed. To accurately determine the relationship between blood pressure and pulse-wave propagation information, it is desirable that a difference between two blood pressure values included in the two combinations of blood pressure value and pulse-wave propagation information be sufficiently large. However, the above blood pressure monitor apparatus cannot accurately determine the relationship between blood pressure and pulse-wave propagation information if a second blood pressure measurement using a cuff which follows a first blood pressure measurement is carried out independent of an actual blood pressure level of the subject. Otherwise, if a blood pressure measurement using a cuff is repeated until a sufficiently large difference between two blood pressure values is obtained, the subject will feel uncomfortable because of the repeated pressing of the cuff.